An human limb prosthesis is typically custom made for each amputee by a prosthetist. The prosthesis consists of various functional components, such as a foot and knee, fastened to the amputee's body by way of a receptacle which accepts the amputee's residual limb. The receptacle is called a socket. The most critical aspect of a prosthesis is the fit of the socket. It must be comfortable and supportive. If the socket does not fit properly, the result can be pain, injury to the skin, poor function of the prosthesis or any combination of these problems. The socket is typically made from a mold or impression of the residual limb. The mold may be modified by the prosthetist to relieve potential pressure by the socket on boney or pressure sensitive areas. The mold is then used to make a diagnostic socket, also referred to as a test socket. The test socket is made of a clear rigid plastic material. The test socket is then attached to the functional components and the amputee can try the prosthesis. Both the amputee and the prosthetist use this test socket fitting as an opportunity to determine the existence of any problems in the fit of the socket. The amputee by report pain or the prosthetist may observe skin discoloration in the test socket due to improper or uneven pressures between the socket and the residual limb. When socket problems are identified, the test socket can be adjusted by heating and reforming a spot in the plastic socket or sanding an area in the plastic.
From U.S. Pat. No. 6,136,039 and US 2009/0240344 A1 a prosthetic liner is known that consists of two or more layers. These layers can be made from polymeric material, silicone or other elastomeric materials. These liners are supposed to increase the wearing comfort for the wearer when the liner is used to couple a prosthesis socket to an amputation limb.
From U.S. Pat. No. 7,377,944 B2 and U.S. Pat. No. 7,780,741 B2 it is known to use a prosthetic liner to hold a variety of different sensors to monitor the physiological health of the enclosed limb. The sensor can be included in the liner material or in a channel formed between an inner layer and an outer layer of the respective liner. The sensors can be for example temperature sensors, humidity sensors, sensors to measure blood pressure, glucose or body fat.
It is often very difficult to identify precisely where the improper pressures are for several reasons:                a) The amputee may feel discomfort but not be able to describe exactly where it is coming from in the prosthesis.        b) The amputee may have poor sensation and not be able to feel discomfort though pressures may exist that can cause damage to the skin. In this case the amputee cannot describe the origin of the pain in the prosthesis.        c) Usually the amputee wears a liner or interface between the skin and the socket for comfort or function. This interface prevents the prosthetist from observing the skin through the clear test socket.        
An orthopaedic brace is properly called an orthosis. Many orthoses require a precise fit to the body surface of the user. For the same reasons as in the case of prosthetic fitting, assessing the fit of a brace can be challenging with the limited tools and materials available.
There are numerous other instances where it is important to assess the pressure against the skin such as in fitting wheelchair cushion, an arch support, or shoes.